Glossary of Terms

These are words that you may encounter when reading information about leukodystrophy:

Allele: One member of a pair of genes that occupy a specific position on a specific chromosome.

Anosmia: Loss of the sense of smell.

Arteriopathy: Disease of the arteries.

Asparatoacylase: The ASPA gene provides instructions for making an enzyme called Aspartoacylase. This gene is responsible for Canavan disease. It is involved in the breakdown of a molecule called NAA, a molecule that is thought to be involved in the removal of water from certain types of brain cells, as well as in the formation of myelin lipids.

Astrocyte: A type of glial cell that provides physical and nutritional support for neurons. Their primary functions include cleaning up brain “debris,” transporting nutrients to neurons, and holding neurons in place.

Ataxia: Disturbance of gait or coordination(s) or wobbliness.

Autosome: All of the chromsomes that are not the sex chromosomes (i.e., x and y chromosomes).

Axon: A physical projection of the neuron cell body that is responsible for carrying signals away from the neuron.

Carrier:

Could refer to an asymptomatic carrier, a person or organism infected with an infectious disease agent, but displays no symptoms.

Genetic carrier, a person or organism that has inherited a genetic trait or mutation, but displays no symptom(s).

Cataract: Clouding over the lens of the eye, impairs normal vision.

Cerebellar Ataxia: Ataxia is wobbliness. Cerebellar ataxia refers to the fact that the defect is in a specific part of the brain (the cerebellum), and the incoordination and unsteadiness is due to the brain’s failure to regulate the body’s posture, as well as the strength and direction of the body’s movements.

Chromosome: A linear strand of DNA that contains many genes; there are 46 human chromosomes (22 pairs of chromsomes, and the sex chromosomes X and Y).

Central Nervous System (CNS): Consists of the brain and the spinal cord. It controls thought processes, guides movement, and registers sensations throughout the body.

Craniofacial Dysmorphism: Refers to an abnormality of the face and/or the head. Craniofacial dysmorphism can include abnormal growth patterns of the face or skull, and may involve the soft tissue as well as the bones. In the case of 18q-syndrome, craniofacial abnormalities will most likely include deep-set eyes, a “carp-shaped” mouth, microcephaly (small head), prominent ears, and midfacial hypoplasia (underdeveloped midfacial regions).

Dendrite: A physical projection of the neuron cell body that is responsible for carrying signals to the neuron.

Dominant Inheritance: A method of genetic inheritance, whereby a single abnormal copy of a gene causes disease, even though a good copy of the gene is also present.

Dystonia: Neurological disorder characterized by involuntary muscle contractions; can affect any part of the body.

Epiphyseal Dysplasia: The epiphysis is the growth area at the end of a bone, while dysplasia means abnormal formation. This means that patients with Refsum disease often have a shortened fourth toe.

Epicanthus: A fold of skin that comes in across the inner angle of the eye, common in children with birth defects such as Down syndrome.

Exome Sequencing (aka Whole Exome Sequencing): A genomic technique for sequencing all of the protein-coding regions of genes in a genome. It consists of two steps: the first step is to select only the subset of DNA that encodes proteins.

Failure to thrive: A general term meaning the child is not growing and gaining weight at the expected rate.

Fluorescent in situ Hybridization (FISH): A method of visualizing chromosomes that can allow scientists to look for gross chromosomal abnormalities.

Fontanelle: The baby’s “soft spot”.

Galactocerebrosidase: Also called GALC, this is a lysosomal protein. Mutations in this gene have been associated with Krabbe disease, also known as globoid cell leukodystrophy.

Genital Hypoplasia: Incomplete development of the genitals.

Genome: Genetic material of an organism. The genome of an organism is the whole of its hereditary information encoded in its DNA. This includes both the genes and the non-coding sequences of the DNA.

Genomic medicine: An emerging medical discipline that involves using genomic information about an individual as part of their clinical care (e.g. for diagnostic or therapeutic decision-making) and the health outcomes and policy implications of that clinical use.

Glaucoma: An eye condition in which the fluid pressure inside the eyes is high, which may damage the eye and lead to vision loss.

Glial Cell: A specialized type of cell that is a “helper” to neurons and is necessary for the proper function of the nervous system. There are several types of glial cells, including astrocytes, microglia, oligodendroglia, satellite cells, and Schwann cells (see the individual defintions of these subtypes of glial cells for more information).

Globoid Cells: A specific type of cell (called the macrophage) accumulates high levels of undegraded galactolipids as a result of the lack of GALC activity in globoid cell leukodystrophy.

Granular Osmiophilic Material: Also called GOM, it is a granular material that accumulates in patients with CADASIL disease.

Hepatomegaly: Enlarged liver.

Hydrocephaly: Literally means “water on the brain.” Characterized by the accumulation of fluid in the brain or between the brain and the skull, it can cause pressure on the brain, resulting in developmental defects. It can also lead to an abnormally large head size (to greater than 90% of normal).

Hyperextension of the Limbs: Limbs are kept abnormally straight.

Hyporeflexia: Slow reflexes.

Hypotonia: Poor muscle tone.

Icthyosis: Icthyosis is a noninflammatory scaliness of the skin. These symptoms can range anywhere from scaliness of the palms and soles of the feet to scaliness on the trunk of the body.

Infarcts: Areas of tissue that have undergone a type of cell death called necrosis, as a result of restricted blood supply.

Ischemic Episodes: Resulting from low oxygen in the blood or tissues, generally as a result of an obstruction of the arterial blood flow.

Leukodystrophy: The word leukodystrophy comes from the Greek words leuko (meaning white), trophy (meaning growth), and dys (meaning ill). The word leukodystrophy describes a set of diseases that affect the growth or maintenance of the white matter (myelin).

Leukoencephalitis: Acute hemorrhagic leukoencephalitis is a rare acute inflammatory myelinopathy of central nervous system with high mortality.

Leukoencephalopathy: A type of change associated with the white matter, which includes localized areas of cell death.

Magnetic Resonance Imaging (MRI): An imaging technique that can be used to visualize any/all parts of the body.

Macroencaphaly/Megalencephaly: Abnormally large brain; this can lead to delayed development, convulsive disorders, corticospinal (brain cortex and spinal cord) dysfunction, and seizures.

Microglia: A type of glial cell that is involved in the digestion of dead neurons.

Micrognathia: Small chin, sometimes called mandibular hypoplasia.

Migraine with Aura: A vascular headache resulting from changes in the sizes of the arteries in the brain. An aura refers to an abnormal sensation that the migraine is going to occur.

Muscle Flexion: Muscles tend to be kept flexed.

Myelin: Myelin, sometimes referred to as “white matter” because of its white, fatty appearance, protects and insulates the axons. It consists of a protective sheath of many different molecules that include both lipids (fatty molecules) and proteins. This protective sheath acts in a manner similar to that of the protective insulation that surrounds an electric wire. It is necessary for the rapid transmission of electrical signals between neurons. It does this primarily by containing the electrical molecules (called ions) within the axon, so that they are properly transmitted to the next neurons.

Myelin Basic Protein (MBP): A protein believed to be important in the myelination of nerves in the nervous system; the gene thought to be associated with 18q-Syndrome or at least for the leukodystrophy aspects of the syndrome.

N-acetyl-L-aspartate: Also called NAA., this molecule is involved in the removal of water from certain types of brain cells, as well as in the formation of myelin lipids. It is involved in the pathology of Canavan Disease.

Neuron: Also called “nerve cells,” the neurons are responsible for transmitting messages throughout the body. They are important in both involuntary function, like the heartbeat, and voluntary functions. like walking.

Notch3 (Notch Receptor 3): A Protein Coding gene and is the gene associated with CADASIL disease, which is involved in determining cell fate.

Nystagmus: Rapid rhythmic repetitious involuntary eye movements.

Occiput: The occiput is the bone forming the back of the skull and encloses the hole where the spinal cord reaches the brain.

Oligodendroglia: A type of glial cell that provides the insulation (myelin) to axons in the central nervous system.

Orbital Ridge: The bony ridge beneath the eyebrow.

Peripheral Nervous System (PNS): Consists of the nerves throughout the body with the exception of those in the Central Nervous System (brain and spinal cord). These include the sensory neurons, which detect any sensory stimuli and alert the CNS of their presence, and motor neurons, which connect the CNS to the muscles and carry out instructions from the CNS for movement.

Peroxisome: A membrane-bound compartment in the cell that is responsible for the breakdown of certain types of fatty acids.

Peripheral Polyneuropathy: This is the term for dysfunction of the nerves outside of the brain and spinal cord. Symptoms may include numbness, weakness, burning pain, and loss of reflexes.

Quadriplegia: Complete paralysis of the body from the neck down.

Recessive Inheritance: A mode of genetic inheritance whereby an affected person must have a pair of dysfunctional forms of the gene to cause the disease. People with only one abnormal gene in the pair are called Carriers and not often affected with a condition. However, they can pass the gene down to their children.

Retinitis Pigmentosa: A disease of the eye, resulting from degeneration of a part of the eye called the retina. It affects night vision and peripheral vision, and eventually can lead to blindness.

Rosenthal Fibers: Abnormal, fibrous deposits present in the CNS that are characteristic of Alexander Disease.

Satellite cells: A type of glial cell that provides physical support to the neurons.

Schwann Cells: A type of glial cell that provides the insulation (myelin) to neurons in the peripheral nervous system.

Seizure: The brain controls how the body moves by sending electrical signals. Seizures (also called convulsions) occur when the normal signals from the brain are changed. Severity of a seizure can vary dramatically. Some people may only shake slightly and do not lose consciousness. Other people may become unconscious and have violent shaking of the entire body.

Spasticity: Tendency to have involuntary muscle contractions due to stiffening or tightening of muscles preventing normal fluid movement.

Subcortical: Relating to the portion of the brain immediately below the cerebral cortex, which is the part of the brain responsible for most higher functions (sensation, voluntary muscle movement, thought, reasoning, memory, etc.).

X-linked Inheritance: A mode of genetic inheritance where the gene responsible for the disease is located on the X chromosome. This means that men are more likely to have the disease than women.